Phase 3 v1: autocheck framework + six step automations

Infrastructure:
- WPH_Step::autocheck($session_state) returns an array of findings
  shaped {id, level: ok/warn/bad/info, label, value, detail}.
- WPH_Session stores results keyed by step id (persisted in the option-
  backed session).
- WPH_Step::has_autocheck() reflection check so the UI only renders the
  panel for steps that implement automation.
- 'Run checks' / 'Refresh' button per step, admin-post handler runs
  autocheck() and stashes the result on the session.
- Findings rendered as a coloured table on the step card; included
  verbatim in the Markdown report with status icons.

Step automations implemented:
- Step 1 (Backup): detection of 11 known backup plugins by slug;
  active/inactive state; UpdraftPlus last-backup timestamp.
- Step 2 (Environment): PHP version + EOL, WP version vs latest, disk
  usage, wp-config flags, file perms on wp-config/wp-content/uploads,
  error-log sizes.
- Step 4 (Plugins): WP.org API enrichment with 24h transient cache —
  last_updated, active_installs, abandonment flag, removed-from-repo
  flag, update-available count. Summary line at the top.
- Step 8 (Security): SSL cert expiry via stream_socket_client +
  openssl_x509_parse, administrator audit, xmlrpc reachability, login
  URL hardening detection.
- Step 9 (Database): spam comments, post revisions, autoload size (WP
  6.6+ value handling), top 3 largest tables.
- Step 11 (Small fixes): deactivated-but-installed plugin list,
  homepage alt-text scan.

Smoke-tested on testsite — all six steps return findings with
correctly-classified levels. Report regenerated with automated findings
section.

includes/class-wph-session.php

@@ -90,6 +90,20 @@ final class WPH_Session {
         update_option(WPH_OPT_SESSION, $this->data, false);
     }
 
+    /** Store the result of running autocheck() on a step. */
+    public function set_autocheck(string $step_id, array $findings): void {
+        $this->data['autocheck'][$step_id] = [
+            'checked_at' => time(),
+            'findings'   => $findings,
+        ];
+        update_option(WPH_OPT_SESSION, $this->data, false);
+    }
+
+    /** Returns ['checked_at'=>int, 'findings'=>array] or null. */
+    public function get_autocheck(string $step_id): ?array {
+        return $this->data['autocheck'][$step_id] ?? null;
+    }
+
     public function progress(): array {
         $steps = WPH_Steps::instance()->all();
         $total = count($steps);